The present invention relates to coupling devices of the type used to transmit torque, for example, in a vehicle driveline, and more particularly, to such coupling devices of the type including a fluid pressure operated clutch assembly for controlling the transmission of torque through the coupling device.
As used herein, the term “coupling device” will be understood to mean and include a device which is able to transmit torque from an input to one or more outputs, and in which there is a clutch assembly disposed in the “torque path” between the input and the output, such that the amount of torque transmitted is a function of the extent of engagement of the clutch assembly. Within the scope of the present invention, the term “coupling device” will further be understood to mean and include both gear-type devices (such as differentials), as well as gearless-type couplings.
Although the present invention may be utilized in conjunctions with many different types and configurations of gearless-type coupling devices, such as a coupling made in accordance with the teachings of U.S. Pat. No. 5,964,126, assigned to the assignee of the present invention and incorporated herein by reference, it is especially advantageous when utilized in conjunction with gear-type vehicle differentials of the general type illustrated and described in U.S. Pat. Nos. 5,310,388 and 6,464,056, both of which are also assigned to the assignee of the present invention and incorporated herein by reference. However, the coupling device of the present invention will differ from the devices of the above-incorporated patents in one important aspect, to be illustrated and described subsequently herein.
In the differential coupling devices of the above-incorporated patents, there is a clutch pack operable to transmit torque between the input (a housing connected to the ring gear) and the output (one of the axle shafts), with the degree of engagement of the clutch pack being determined by the fluid pressure in a clutch apply chamber. The fluid pressure biases a clutch apply (or engagement) member (such as a piston) against the clutch pack. The differential coupling device of the cited patents includes a gerotor pump having one rotor fixed to rotate with the coupling device input, and the other rotor fixed to rotate with an output of the coupling device, such that the flow of pressurized fluid into the clutch apply chamber is generally proportional to the speed difference between the input and the output. As used herein, the term “clutch pack” will be understood to mean and include both a multiple friction disk type clutch pack, as well as any of the other well known types of clutch assemblies, such as cone clutches, in which the degree of engagement is generally proportional to the fluid pressure acting on the clutch piston or on an equivalent clutch-engagement device or structure.
In differential coupling devices of the type to which the present invention relates, it is typical to provide a fluid flow path from the clutch apply chamber to a reservoir or some other “source” of low pressure fluid, and to provide, as part of this “main” flow path, some sort of control valve which can control the flow from the clutch apply chamber to the low pressure source. In this manner it is possible to control the pressure in the clutch apply chamber, and therefore, control the “bias torque”, i.e., the extent to which torque is transmitted from the input to the output. In the differential coupling devices of the above-incorporated patents, in which the pump assembly rotates at a speed representative of the speed difference between the input and the output of the coupling device, it will be understood by those skilled in the art that, not until a certain, predetermined speed differential (input “minus” output) occurs, will there be enough pressure build-up in the clutch apply chamber to generate the desired bias torque.
A commercial embodiment of a differential coupling device of the general type to which the present invention relates, but including the “conventional” pump arrangement is illustrated and described in co-pending application U.S. Ser. No. 10/964,134, Filed Oct. 13, 2004 in the names of Celso L. Fratta, Robert J. Kyle, Keith E. Morgensai, and Patrick J. McMillan, for a “Coupling Device And Improved Fluid Pressure System Therefore”. It has been observed that in this commercially developed differential coupling device, a typical “time to engagement” is in the range of about 300 milliseconds, with a differential speed across the coupling device of approximately 150 rpm. Although such a response time may be more than satisfactory for many applications for such differential coupling devices, especially when the devices are merely performing conventional “slip limiting” functions, to achieve basic traction control, there are now many other potential applications in which such a response time is clearly not acceptable. For example, if the same, basic coupling device were being used as part of a stability control system, it is anticipated that the required response time (time to engagement) would need to be somewhere in the range of about 50 milliseconds.
It is known to provide a differential coupling device in a vehicle driveline, wherein the device includes a hydraulic pressure-operated clutch and apply arrangement, wherein the source of the hydraulic pressure used to apply the clutch was a pump disposed “remotely” relative to the differential coupling device, with the pump having “full-time” drive. For example, such an arrangement is known in which the pump is driven off the main driveline prop-shaft of the vehicle. Thus, there is a constant source of hydraulic energy available to actuate the clutch, but the typical, remote location results in some fairly awkward packaging and mounting arrangements.